The present invention relates to a process for separating cobalt and nickel from a solution containing cobalt and nickel by liquid-liquid extraction using a specific organic phosphorus compound.
Generally, serious drawbacks are observed in a conventional liquid-liquid extraction process wherein cobalt is selectively extracted into an organic phase containing an extractant in that the viscosity of the organic phase will rise up to more than 150 cSt hindering mixing of an extraction system and pumping, since a solution containing cobalt and nickel to be treated ("raw solution" hereinafter) has a relatively high cobalt concentration, thus an extracted cobalt being largely accumulated in the organic phase at an initial extraction stage, i.e. at the initial contact stage of the raw solution with the organic extraction medium. In such an industrial extraction process, there is usually dissolved iron in the extraction system, whereby the viscosity of the organic extraction medium will rise still higher. Such drawbacks prevent one from applying an extractant even capable of pronounced selective extraction of cobalt.